The AEC Routemaster is a double-decker bus that was introduced by AEC in 1954 and produced until 1968. Primarily front-engined, rear open platform buses, a small number of variants were produced with front entrances and/or doors. Entering service in 1956, the Routemaster saw continuous service in London until 2005, and currently remains on two heritage routes in central London.

Having been developed in partnership with London Transport, the customer of nearly all new Routemasters was to be that organisation, in both traditional red and green "country" colours, although small numbers were also delivered new to British European Airways and The Northern General Transport Company. In all, 2876 Routemasters were built, with approximately 1000 still in existence.

A pioneering design, the Routemaster outlasted several of its replacement types in London, survived the privatisation of the former London Transport bus operators, and saw proliferation to other operators around the UK. Latterly in modern UK public transport bus operation, the unique features of the standard Routemaster attracted both praise and criticism alike. Notably the open platform, while open to the elements, allowed boarding/alighting away from stops; and the presence of a conductor allowed minimal boarding time and security, although conductors perpetuated higher labour costs and increased the effect of labour shortages.

The image of the traditional red Routemaster has become one of the famous icons of London, with much tourist paraphernalia continuing to bear Routemaster imagery, and examples still in existence around the world. Despite its iconic status, the previous London bus classes the Routemaster replaced (the RT-type AEC Regent and Leyland Titan RTL and RTW counterparts) are usually mistaken for Routemasters by the public and by the media, along with any other red half-cab in some cases!